In many contemporary mechanical systems such as valves, dampers, etc., an electro-mechanical actuation system is used to transition the mechanical system from one state to another. For example, a traditional ball valve or butterfly valve may have an electro-mechanical actuator attached to the valve stem thereof and operable to rotate the valve stem such that the valve is transitioned between a closed position and an open position.
Given that electro-mechanical actuators require a power supply, the actuator will fail to provide the desired actuation in the event of a power failure. As a result, many electro-mechanical actuators are often supplied with a mechanical override or fail-safe device that returns the valve to a default position in the event of a power failure. For example, an electro-mechanical actuator can be configured to return a valve to a normally closed or normally open state once the power supply of the electro-mechanical actuator fails. Such functionality is desirable in applications where a position of the valve, e.g. open or closed, is preferred only when power is present in the system.
However, in fail-safe type valve actuators, once the actuator loses power the valve returns to its default position, and it will remain in that state until power is restored to the valve actuator. As a result, the valve coupled to the valve actuator is confined to whatever default position the valve actuator is designed to return the valve to in the event of a power failure. In certain instances, however, it is desirable to maintain the valve coupled to the valve actuator in its pre-power failure state. For example, in a system configured with a fail-safe type valve actuator, it is desirable in some instances to place the valve in a pre-power failure state despite the continued absence of power so as to enable troubleshooting of the system. For another example, it may also be desirable to place a valve in a position other than the predetermined position defined by the fail-safe device during initial installation when no power supply is present.
Embodiments of the present invention relate to improvements in the art of valve actuators as discussed above. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.